There are many prior art solutions and methods for filling the ink reservoir with ink.
Amongst the various systems commonly used, with the passage of time the use of vacuum filling became established, due to its practicality and effectiveness.
The system involves filling by creating a vacuum inside the pen body so that the ink is sucked in by it.
The most used method involves syringe filling, which uses the more classic method for creating a vacuum: that of moving a plunger backwards in a cylindrical hollow body, precisely as occurs for syringes.
That system is simple to make from a mechanical viewpoint and is usually made with a shaft inserted through a hole in the end part of the pen.
At the other end of the shaft, inserted in the pen body, a seal is mounted.
Filling is performed by accessing the shaft from the rear of the pen and pushing it as far as it will go, then sucking in the ink, exactly as occurs with a syringe, by pulling the shaft backwards.
The most used mechanism for the movement of the shaft/plunger is of the male and female screw type.
Turning the end part of the pen (the bottom) makes the shaft/plunger move forwards or backwards and causes consequent emptying/filling of the ink from/to the inside of the ink reservoir.
Like any cylinder-piston type connection, prolonged use compromises the seal between the two components, causing unwanted ink leaks, with the obvious risk that ink may get out of the ink reservoir.
Moreover, fountain pens comprise a nib in fluid communication with the ink reservoir through a channel which allows the ink to pass from the ink reservoir to the nib.
Some such pens also comprise a nib closing cap which is applied to the end of the barrel after the pen has been used.
Ink is often leaked from the channel connecting the ink reservoir to the nib, even when the pen is not used and the cap is applied to the barrel.
Such leaks are more frequent if the pen is in environments in which the temperature or the pressure vary, for example during aeroplane flights.
Leaks cause unwanted marks on clothing (for example, a shirt or jacket pocket) or the containers where the pen is put away.